How can I calculate global coordinates for GPencilStrokePoint in Blender 2.8 and Python?
The following script prints the global point coordinates for every grease pencil object in the scene. The coordinates seem to be accurate, judging from basic tests.

import bpy


for obj in bpy.data.objects:
    if obj.type == "GPENCIL":
        print(f"\n{obj.name}")
        for layer in obj.data.layers:
            for frame in layer.frames:
                for stroke in frame.strokes:
                    for point in stroke.points:
                        print(obj.matrix_world @ point.co)